Remove x86_64 x25519 assembly.
Now that we have 64-bit C code, courtesy of fiat-crypto, the tradeoff
for carrying the assembly changes:
Assembly:
Did 16000 Curve25519 base-point multiplication operations in 1059932us (15095.3 ops/sec)
Did 16000 Curve25519 arbitrary point multiplication operations in 1060023us (15094.0 ops/sec)
fiat64:
Did 39000 Curve25519 base-point multiplication operations in 1004712us (38817.1 ops/sec)
Did 14000 Curve25519 arbitrary point multiplication operations in 1006827us (13905.1 ops/sec)
The assembly is still about 9% faster than fiat64, but fiat64 gets to
use the Ed25519 tables for the base point multiplication, so overall it
is actually faster to disable the assembly:
>>> 1/(1/15094.0 + 1/15095.3)
7547.324986004976
>>> 1/(1/38817.1 + 1/13905.1)
10237.73016319501
(At the cost of touching a 30kB table.)
The assembly implementation is no longer pulling its weight. Remove it
and use the fiat code in all build configurations.
Change-Id: Id736873177d5568bb16ea06994b9fcb1af104e33
Reviewed-on: https://boringssl-review.googlesource.com/25524
Reviewed-by: Adam Langley <agl@google.com>

BoringSSL

BoringSSL is a fork of OpenSSL that is designed to meet Google's needs.

Although BoringSSL is an open source project, it is not intended for general use, as OpenSSL is. We don't recommend that third parties depend upon it. Doing so is likely to be frustrating because there are no guarantees of API or ABI stability.

Programs ship their own copies of BoringSSL when they use it and we update everything as needed when deciding to make API changes. This allows us to mostly avoid compromises in the name of compatibility. It works for us, but it may not work for you.

BoringSSL arose because Google used OpenSSL for many years in various ways and, over time, built up a large number of patches that were maintained while tracking upstream OpenSSL. As Google's product portfolio became more complex, more copies of OpenSSL sprung up and the effort involved in maintaining all these patches in multiple places was growing steadily.

Currently BoringSSL is the SSL library in Chrome/Chromium, Android (but it's not part of the NDK) and a number of other apps/programs.